#include <cstdio>
#include <algorithm>

using namespace std;

int a[ 1500 ];

int main( )
{
    int i, n, p;
    while ( scanf("%d", &n) && n )
    {
        for ( i = 0; i < n; i++ )
            scanf("%d", &a[ i ]);
        p = 0;
        sort( a, a + n );
        for ( i = 0; i < n; i++ )
            if ( a[ i ] - p > 200 )
                break;
            else
                p = a[ i ];
        if ( i < n )
        {
            puts("IMPOSSIBLE");
            continue;
        }
        for ( i = n - 1; i >= 0; i-- )
            if ( 2844 - a[ i ] - p > 200 )
                break;
            else
                p = 2844 - a[ i ];
        if ( i < 0 && p >= 2644 )
            puts("POSSIBLE");
        else
            puts("IMPOSSIBLE");
    }
    return 0;
}
